Actuators typically are mechanical devices that are used for moving or controlling a mechanism or system and typically convert energy into some type of motion. Examples of actuators can be found in any number of applications encountered in every day life including automotive, aviation, construction, farming, factories, robots, health care, and prosthetics, among other areas.
Every mechanical system designed to move or control a mechanism or system must have one or more “prime movers” to provide the work needed and one or more “transmissions” to convey the work from the prime mover to the object that is desired to be moved. Prime movers typically convert electrical or chemical energy to mechanical energy in the form of forces and displacements.
Examples of prime movers may include combustion engines, electric motors, biological/artificial muscles, piezo-electrics, shape-memory-alloys, magnetostrictives and dielectrics, among others. Examples of transmissions may include levers, linkages, wheels, gears, pneumatics and hydraulics, among others.
Hydraulic systems are generally known and typically include an actuator and one or more valves in fluid communication with a pump that provides fluid to the system at a fixed pressure. Such systems tend to be very inefficient, costly and noisy. This is particularly true in hydraulic systems that rely on “throttling” of fluid through a valve to provide control in the system where fluid is transitioned from high to low pressure without extracting the energy as useful work but instead wasting that energy primarily in the form of heat.
Compliant control or impedance control is sometimes desirable in mechanical devices to provide an amount of “give” or reduced stiffness in the operation of the device. Existing active compliance control systems, however, typically require expending additional energy to reduce operational stiffness which is undesirable in most if not all applications.